Ambient vibration recordings used to map glaciers thickness - A first study from alpine glaciers

The application of geophysical techniques on glaciers can be very useful to study the overall impact of climate changes on the terrestrial cryosphere. The multichannel seismic and GPR (ground penetrating radar) methods are the most popular and widely geophysical techniques used in glaciology. Besides enabling to monitor the glacier thickness and then the ice mass balance, these methods can provide useful information on the basal sediment properties, which influence the overall glacier flow. However, these methods require considerable economic and operational efforts, and can be used only where the logistical difficulties are easily overcome. Passive seismics can help to solve this problem, by using broadband seismometers and the HVSR method. Microtremor measurements and the Nakamura's HVSR (Horizontal to vertical spectral ratio) technique, generally used for site-effect studies as well as to determine the thickness of soft sediment layers, can be effectively used to map the thickness of glaciers. The application of the HVSR technique on glaciers, requiring less economic and operational efforts, may allow to avoid most of the logistical difficulties characterizing the active seismic and GPR methods in these extreme environments. The great advantage of passive seismic tools, in addition to the reduced size and weight, is that there is no need of an active source of elastic waves. In fact, taking advantage of the ambient noise, they does not require the use of artificial sources such as explosives, which are usually detonated in boreholes to be drilled using hot water. Here we present the results of some tests regarding the reliability of the HVSR method on ice, which have been successfully carried out on some Alpine glaciers